Use of dunder in concrete compositions

ABSTRACT

A cementitious mixture for concrete including an admixture including dunder having a solids content in a range of from 5% to substantially 100% by weight, the dunder being added to the cement in a range of from 0.1% to 5% by weight of cement in a concentration which results in the initial setting time being less than thirty-six hours.

FIELD OF INVENTION

THIS INVENTION relates to an admixture for cementitious mixtures and toa method of forming cementitious mixtures.

The present invention has particular application to admixtures forreducing the water requirement, extending the setting time, and/orimproving the properties of cementitious mixtures in the fresh or“plastic” and hardened states.

BACKGROUND ART

Admixtures have been added to cementitious mixtures to improve theirproperties. Better flow characteristics of the cementitious mixturesprior to setting increases density of the casting, reducing undesirablevoids, and reducing the water requirement increases the strength of theconcrete. Delaying the setting time is also desirable in somecircumstances, particularly in warmer climates.

Lignin and/or lignin related compounds have traditionally been used asadmixtures for cementitious mixtures. However, lignin has recentlybecome quite expensive, and is in short supply. Other substitutes havebeen tried, but have been found not to perform as required, and/or notbeen cost effective. Substitutes can be, and often are, added to ligninbased admixtures, but this practice, though extending the lignin base,results in less than maximum improvement obtained with unadulteratedlignin based admixtures and/or is expensive. Molasses is often orsometimes used as a substitute for lignin. However, it is generallyaccepted that molasses does not perform as required by itself and is notsuitable itself as a water reducing admixture to cementitious mixtures.Against this background, it has been surprisingly found that dunderperforms adequately as an admixture for cementitious mixtures, and ifmodified in accordance with the invention described hereinafter, obtainsequal or superior results when compared with ordinary lignin. In thisspecification, unless the context requires otherwise, dunder includesany residuum obtained after distillation of molasses or sugar productsuch as vinasse and the like. In this specification, unless the contextrequires otherwise, the terms “cementitious mixture” and “concrete” aretaken to include concrete, shotcrete, mortars, grouts and similarcementitious compounds including mine tailing (backfill). Generally, theterm cement refers to a compound which is soft when first prepared butsets or hardens. In the case of cementitious mixtures, cement becomesplastic after the addition of water, after which the mixture sets. Inthis specification, unless the context requires otherwise, the term“cementitious mixture” refers to the workable liquid which can solidifyto form mortar or concrete. In this specification, the term “Portlandcementitious mixture” refers to a combination of cementitious materialswhich consist of the active ingredients and binders and to which sand,aggregate and/or other additives may be added with water to form acement paste, mortar or concrete.

The present invention aims to provide an admixture for cementitiousmixtures, and a method of forming cementitious mixtures, which alleviateat least one of the shortcomings of the prior art, or at least toprovide an alternative to currently used admixtures for cementitiousmixtures. Other aims and advantages of the invention may become apparentfrom the following description.

DISCLOSURE OF THE INVENTION

With the foregoing in view, the present invention resides broadly in anadmixture formulation for cementitious mixtures including dunder havinga solids content in a range of from 5% to 100% by weight.

In another aspect, the present invention resides broadly in acementitious mixture for concrete, said cementitious mixture includingan admixture including dunder, said dunder having a solids content in arange of from 5% to 100% by weight, and said dunder being added to thecement in a range of from 0.1% to 5% by weight of cement in aconcentration at which the initial setting time is less than thirty-sixhours.

Preferably, the limit of addition of dunder is selected such that theinitial setting time is less than twenty-four hours. More preferably,the limit of addition of dunder is selected similar to that of astandard lignin such that the initial setting time is less than ninehours.

It will be appreciated that solids content equates to a measurement onthe Brix Scale and also to specific gravity, which can usually be moreeasily measured. Accordingly, these alternative units converted tosolids content may be used and the invention extends to dunder havingequivalent brix or specific gravity.

The acidity of the dunder may be modified, if so required, typically tobe within the pH range of from 3 to 7 for use in cementitious mixtures.If desired, further additives may be added to or combined with dunder toadjust the retardation of setting time and provide a more stablesolution, such as, but not limited to, caustic soda.

In another aspect, the present invention resides broadly in a method offorming cementitious mixtures including:

forming a dry mix from Portland cementitious binders, aggregate and/orsand;

combining the dry mix with an amount of water sufficient to form anaqueous phase; and

adding dunder during or after the formation of the aqueous phase toachieve a slump value in the range of 0 mm to 275 mm.

If required, more water may be added to the mixture to achieve theaforementioned range of slump values.

Preferably, the moisture content of the dunder is reduced as describedherein. If desired, the acidity of the dunder may be adjusted by theaddition of alkali such as, for example, caustic soda or an equivalent.

Preferably, the solids content of the dunder is increased by evaporationor spray drying, although alternative forms of drying may be employed,such as, for example, freeze drying, or the like to improve the storage,handling, and subsequent performance of the dunder admixtures.

BRIEF DESCRIPTION OF THE EXAMPLES

In order that the invention may be more readily understood and put intopractical effect, reference will now be made to three examples whichillustrate the invention in one or more preferred forms, and wherein:

-   -   Example 1 illustrates the water reducing effect of the admixture        of dunder according to the invention;    -   Example 2 illustrates schematically the performance of a range        of several cementitious mixtures according to the invention        against a control cementitious mixture; and    -   Example 3 illustrates schematically the use of dunder at a range        of admixture dosages in cementitious mixtures according to the        invention in comparison with untreated mixtures and mixtures        according to the prior art.

DETAILED DESCRIPTION OF THE EXAMPLES Example 1

A control concrete mix was prepared by weighing and combining thefollowing components in a free fall drum mixer to form a control drycement mix:

Portland cement 380 kg fine aggregate 760 kg course aggregate 950 kg

Water was weighed, added to and mixed with the control dry concrete mixuntil uniform in workability and colour and until a slump value, bymeasurement, of 150 mm was obtained. The total water requirement wasfound to be 215 kg for the control concrete mix (the “control waterrequirement”) at that slump value.

From the above amounts, the water/cement ratio was determined to be0.566 by dividing 215 kg by 380 kg. The ratio of materials by weight ofcement was calculated to be 1.0:2.0:2.5:0.566. The sum of the ratios wastherefore 6.066. The plastic density of the control cement mix wasdetermined to be 2,305 kg/m³. The density divided by the sum of ratioswas 2,305/6.066 or:

Portland cement 380 kg fine aggregate 760 kg course aggregate 950 kgwater 215 kg total 2,305 kg  

A test concrete mix was prepared using the same quantities of Portlandcement, fine aggregate and course aggregate as in the case of thecontrol cement mix to form a test dry concrete mix. Dunder, having adensity of 13.7 brix and a specific gravity of about 1.05, was added tothe test dry cement mix at a rate of 1.75 kg of dunder per 100 kg ofcement after about 80% of the control water requirement had been addedwith further amounts of measured water added until a slump value, bymeasurement, of 150 mm was obtained. The total water requirementincluding the water contained in the dunder and any further amounts ofmeasured water added after the addition of the dunder, and thereforeadded to the total water used, was weighed at 200 kg.

From the above amounts, the water/cement ratio was determined to be0.526 by dividing 200 kg by 380 kg. The ratio of materials by weight ofcement was calculated to be 1.0:2.0:2.5:0.526. The sum of the ratios wastherefore 6.026. The plastic density of the control cement mix wasdetermined to be 2,290 kg/m³. The density divided by the sum of ratioswas 2,290/6.026 or:

Portland cement 380 kg fine aggregate 760 kg course aggregate 950 kgwater 200 kg total 2,290 kg  

In this example, therefore, the water reduction due to the addition ofdunder was 7.5% (200 kg+215 kg).

It has been found that higher values of water reduction can be obtainedwith up to, for example, 11.5% water reduction using dunder evaporatedto a higher solids content.

Example 2

For comparison purposes, three cementitious mixtures (options 1, 2 and3) were compared with a control cementitious mixture and the resultstabulated as follows:

Control Option 1 Option 2 Option 3 Cement (kg/m³) 400 400 373 400 Coarseaggregate (kg/m³) 985 1010 1023 985 Fine aggergate (kg/m³) 715 733 743715 Water (kg/m³) 210 188 187 204 Dunder at 13.7 brix (kg/m³) Nil 7 6.57 Water/Cement ratio 0.52 0.48 0.52 0.52 (including water in dunder)Slump (mm) 100 100 100 150 Compression strength (MPa)  1 day 10.5 11.011.5 11.5  3 days 23 26 22.5 23  7 days 35 39 36.5 36 28 days 42.5 47.543 42

Example 3

A trial concrete mix was prepared and various types of admixture andadmixture doses were added to provide the result as follows:

Trial water hours to hours to concrete reduction initial set final setmix percent*** (approx) (approx) Remarks 1^(st) control mix - 0 3+  5+untreated 2^(nd) control mix, 12 6+  7+ benchmark lignin* Dunder at 138+ 10+ equivalent dosage Dunder at 1.5 × 18 12+  13+ equivalent dosageDunder at 2.0 × 23 19+  21–22 Extended equivalent retardation - dosagehigher strength after stiffening**** Dunder at 2.5 × 24 18–19 21–22Extended equivalent retardation - dosage higher strength afterstiffening**** Dunder at 3.0 × 25 24–25 27–28 Extended equivalentretardation - dosage higher strength after stiffening**** *Benchmarklignin added at 0.5% of liquor (approximately 35% solids) by weight ofcement. Commercial lignin source for use in concrete and mortar mixturesused in tests. ** Dunder added at 0.5% of liquor (approximately 35%solids) by weight of cement. ***Water reduction was calculated bydividing water demand of treated mixes by water demand of untreatedcontrol mix. ****All dunder mixes gained strength satisfactorily afterinitial retardation and had superior strength when compared to untreatedcontrol mix at all ages from and including 3 days.

The results indicate that evaporated dunder has superior performance todunder at normal consistency, as stored in sugar processing plants (e.g.at 13.7 brix) based on comparative data from trials. Extendedretardation effects can be reduced by the addition of other materials orblending with non-retarding admixtures. Performance limits for dunderunder various parameters set forth in this specification may be expandedto subjective economic limits, but other technical limitations mayemerge from further research.

From the above, it may be seen that dunder may be used as an alternativeadmixture in concrete mixes providing similar improvements to theconcrete mixes to those provided by lignin. Additionally, it is believedthat dunder also provides a reduced material cost for cement admixtures.

Although the invention has been described with reference to one or morespecific examples, it will be appreciated by those skilled in the artthat the invention may be embodied in other forms within the broad scopeand ambit of the invention as defined by the following claims.

1. A cementitious mixture for concrete, said cementitious mixturecomprising cement and one or more admixtures, said one or moreadmixtures including dunder, said dunder having a solids content in arange of from 5% to substantially 100% by weight, and said dunder beingadded to the cement in a range of from 0.1% to 5% by weight of cement.2. A cementitious mixture according to claim 1, wherein theconcentration of said dunder is selected such that the initial settingtime of the cementitious mixture is less than thirty-six hours.
 3. Acementitious mixture according to claim 2, wherein the concentration ofsaid dunder is selected such that the initial setting time of thecementitious mixture is less than nine hours.
 4. A cementitious mixtureaccording to claim 1, wherein the acidity of the dunder is modified ifso required to be within the pH range of from 3 to
 7. 5. A cementitiousmixture according to claim 1, wherein one or more additives are added toor combined with dunder to adjust the retardation of setting time andprovide a more stable solution of dunder.
 6. A cementitious mixtureaccording to claim 5, wherein one of the additives includes causticsoda.
 7. A method of forming cementitious mixtures including: forming adry mix from Portland cementitious binders, aggregate and/or sand;combining the dry mix with an amount of water sufficient to form anaqueous phase in the mixture; and adding dunder during or after theformation of the aqueous phase to achieve a slump value of thecementitious mixture in the range of 0 mm to 275 mm.
 8. A methodaccording to claim 7, including adding water to the mixture to achievesaid range of slump values.
 9. A method according to claim 7, whereinthe moisture content of the dunder is reduced.
 10. A method according toclaim 7, wherein the acidity of the dunder is reduced by the addition ofalkali.
 11. A method according to claim 7, wherein the solids content ofthe dunder is increased by a drying process.
 12. A method according toclaim 8, wherein the acidity of the dunder is reduced by the addition ofalkali.
 13. A method according to claim 8, wherein the solids content ofthe dunder is increased by a drying process.
 14. A method according toclaim 9, wherein the solids content of the dunder is increased by adrying process.
 15. A cementitious mixture according to claim 2, whereinthe acidity of the dunder is modified if so required to be within the pHrange of from 3 to
 7. 16. A cementitious mixture according to claim 3,wherein the acidity of the dunder is modified if so required to bewithin the pH range of from 3 to
 7. 17. A cementitious mixture accordingto claim 1, wherein the concentration of said dunder is selected suchthat the initial setting time of the cementitious mixture is less thantwenty-four hours.